In connection with more limited access to natural resources such as oil and gas when these resources become smaller and being of less quality efforts are being made to fund New resources or such resources that until now have not been exploited due to excessively high costs for extraction and subsequent processes such as transport and further fabrication of the raw material, maintenance of the resource and measuring operations.
Exploration of oil and gas from the sea bottom in deep se is an established technology. Transport of equipment and goods to and from the source and transmission of signal and energy is managed from the water surface. In very deep waters there might be transport distance that amounts up to 10,000 meters for such applications. Wire, rope or cables of stainless steel is used to a greater extent in applications for off-shore exploration of oil and gas.
So-called wirelines are today usually made in such manner that they contain several isolated electrical leads or cables such as fiber-optical cables which in their entirety are covered by one or several layers of helically extending steel wires. The selection of the steel grade is determined primarily by the demands for strength, ultimate strength and ductility in combination with suitable corrosion properties especially under those conditions valid for oil and gas explorations.
The usage is limited largely due to resistance to fatigue due to repeated use in oil and gas industry, especially when used as slick-line, wire-line or wellbore logging cable and in applications of repeated coiling and transportation over a so-called pulley-wheel. The possibility of usage of the material is limited in thus sector of the ultimate strength of the wire material being used. The degree of cold deformation is usually optimized with regard to the ductility. Specially the austenitic materials do however not satisfy the practical demands.
The latest years, when environments for usage of corrosion resistant metallic materials have become more demanding has caused increased requirements upon the corrosion properties of the material as well as their mechanical properties. Duplex steel alloys, established as alternative for the hitherto used steel alloys such as highly alloyed austenitic steels, nickel base alloys or other highly alloyed steels are not excluded from this development. There are high demands for corrosion resistance when the string, rope. or the line is exposed to high mechanical properties and the very corrosive environment when the surrounding isolation of a plastic material such as polyurethane is damaged and made unusable very quickly during repeated coiling. More recent developments are therefore aimed at using the reinforced wire as the outermost layer.
There is furthermore a desire of significantly higher strength than achieved with today's technology for a certain degree of cold deformation.
The disadvantage with the duplex alloys used today is the existence of hard and brittle intermetallic precipitations in the steel, such as sigma phase, especially after heat treatment during the manufacture or during subsequent working. This leads to harder material with worse workability and finally worse corrosion resistance and possibly crack propagations.
In order to furthermore improve the corrosion resistance of duplex stainless steels it is demanded an increase of the PRE number in both the ferrite as well as in the austenite phase without simultaneously impairing the structure stability or workability of the material. If the analysis in the two phases is not equal with regard to the active alloy constituents one phase will become susceptible for nodular or crevice corrosion. Hence, the more corrosion sensitive phase will govern the resistance of the alloy whereas the structure stability is governed by the most alloyed phase.